Appropriate crowbar protection for improvement of brushless DFIG LVRT during asymmetrical voltage dips

- An equivalent circuit is proposed for analyzing BDFIG behavior during voltage dips.
- Determining the optimum crowbar for riding the BDFIG through asymmetrical faults.
- Protecting the power electronic switches against the over-current and over-voltage.
- Various simulations by using the coupled circuit model show the validity of analysis.

This paper proposes effective approach for determining appropriate crowbar resistance value to be able to improve the brushless doubly fed induction generator ride through capability during any asymmetrical voltage dip scenarios. The brushless DFIG has great potential for wind power plants particularly in offshore applications where maintenance is a major concern. Dynamic behavior of the machine is studied using two axis model and a more precise equivalent circuit model is extracted for analyzing machine behavior under fault conditions.Important limits and constraints in the use of crowbar are identified and discussed in detail. It is shown that large crowbar values can lead to considerable overvoltage which can damage the power electronics converter. Hence, crowbar voltage is an important consideration in crowbar implementation. Efficiency of the crowbar providing ride through capability is investigated for asymmetrical faults by using MATLAB/Simulink for a D180 brushless DFIG prototype.